The present invention relates to a method for coating a substrate with a silicone adhesive-releasing coating, and to the coated substrates obtained therefrom.
Silicone release coatings are well known. Films of cured polyorganosiloxanes provide easy release of a variety of adherent substances. One particularly well-known example of a silicone release coating is silicone-coated release paper. When laminated with pressure sensitive adhesive, (hereinafter also called PSA), silicone coated release paper provides protection for the PSA on, e.g., tapes and labels, and provides subsequent easy release of the coated release paper from the adhesive coating immediately prior to its intended final use, without significant loss of the adhering qualities of said PSA.
While heat-curing silicone coatings furnished as a solution in a volatile hydrocarbon solvent can provide acceptable silicone release coatings, environmental and efficiency considerations have motivated the development of solventless, silicone compositions. Because of the relative safety and low cost of UV radiation sources, methods of curing such solventless silicone compositions with UV radiation have been particularly sought.
Canadian Pat. No. 653,301, discloses an extremely broad class of silicones, other organosilicon polymers, and organosilicon compounds, that are curable by exposure to x-rays, energetic electrons, or UV radiation, with necessary exposure times ranging from a few minutes to several hours. However, exposure times even as short as one minute are unacceptably long for modern release coating application processes.
U.S. Pat. No. 3,726,710, discloses rapid UV radiation curing of silicones containing silicon-bonded vinyl radicals to provide release coatings. U.S. Pat. No. 4,052,529, discloses silicones containing silicon-bonded vinyl radicals and silicon-bonded mercaptoalkyl radicals, to provide UV radiation cured release coatings. British Pat. No. 1,433,461, discloses the UV radiation curing of silicones containing silicon-bonded vinyl radicals and silicon-bonded hydrogen radicals.
The last three patents mentioned above rely upon the use of silicones containing highly reactive substituents, such as vinyl radicals and mercaptoalkyl radicals, to provide rapid cure of a siloxane release coating by exposure to UV radiation.
None of the above references teach the present invention, wherein certain polydiorganosiloxanes without highly reactive substituents can be rapidly cured by exposure to UV radiation. The discovery of the method of the present invention provides economic advantages since the highly reactive substituents of the prior art add significantly to the cost of silicones containing said highly reactive substituents. In addition, the compositions of the method of the present invention generally have enhanced storage stability in comparison to the compositions of the prior art containing highly reactive substituents.